1. Field of the Invention
The invention relates to a woven strip, for use in particular in the papermaking industry, the strip having an asymmetrical weave constituted by weft yarns and warp yarns extending between two opposite ends of the strip, the warp yarns being folded back at each end of the strip and re-woven with weft yarns over a re-weaving zone adjacent to said end so as to form loops.
For example, in the papermaking industry, machines for manufacturing paper continuously generally comprise three sections, respectively a forming section, a press section for extracting water, and a drier section for drying the sheet of paper.
In the drier section of a papermaking machine, the sheet of paper is applied to a set of heated cylinders. To improve the speed with which the sheet of paper dries, it is transported onto the heated cylinders by woven strips (sometimes referred to as drier wires), preferably having an asymmetrical weave, generally comprising round-section weft yarns woven with warp yarns of flat section, the warp yarns defining large floats on the front face of the strip which comes into contact with the sheet of paper. This type of strip serves to reduce the extent to which the sheet of paper is marked by the warp yarns, in a machine configuration in which the strip is constantly in contact with the sheet throughout its sinuous path over two horizontal rows of cylinders.
Furthermore, in a woven strip having an asymmetrical weave constituted by warp yarns defining floats on the front face of the strip, the neutral plane of the strip (the plane in which the strip is subject neither to compression nor to extension when the strip bends) lies between the midplane and the front face of the strip, in the thickness direction thereof. As a result the front face of the strip in contact with the sheet of paper travels at a speed that is substantially constant over the cylinders, thereby having the effect of reducing tension in the sheet of paper and thus reducing the risk of the strip being abraded once the dryness level of the sheet of paper becomes significant, in a machine configuration where the strip is constantly in contact with the sheet throughout the sinuous path of the sheet between the high and low cylinders of the machine.
Each woven strip is configured as an endless belt on being installed on the machine, e.g. by means of a rigid rod which is passed both through loops formed at one end of the strip and through loops firmed at the other end of the strip, with the loops of the two ends being meshed with one another prior to receiving the rod, as is well known. However, when this endless strip is put into operation, under the effect of the tensions acting on the strip while it is being driven, the junction line between the two ends of the strip as constituted by the rod is urged out from the midplane of the strip towards the front face of the strip, with the axis of the rod occupying a position on the neutral plane of the strip. This shift of the strip junction line in the thickness direction of the strip gives rise to excess pressure on the sheet of paper running a significant risk of marking the sheet of paper and of causing the strip to wear quickly. The object of the invention is to remedy those drawbacks.
2. Description of the Related Art Including Information Disclosure Under 37 CFR 1.97 and 1.98 Not Applicable
To this end, the invention provides a woven strip having asymmetrical weave constituted by weft yarns and warp yarns extending between two opposite ends of the strip, the warp yarns being folded back at each end of the strip and re-woven with weft yarns over a re-weaving zone adjacent to said end so as to form loops, the strip being characterized in that each re-weaving zone is of symmetrical weave.
By means of such a structure, the junction line between the opposite ends of the strip is no longer subjected to displacement in the thickness direction of the strip when it is put under tension while configured as an endless belt. In the zones in which the warp yarn is re-woven, the neutral plane of the strip,coincides with its midplane which contains the junction line between the ends of the strip. Furthermore, the gradient of the neutral plane of the strip is spread over the two zones in which the warp yarn is re-woven and is no longer localized on the junction line between the two ends of the strip.
In a particular embodiment of the invention, each symmetrical-weave re-weaving zone adjacent to an end of the strip can be formed by causing the folded-back warp yarns at the ends to take the place of the adjacent warp yarns that have been interrupted prior to the re-weaving zone.
In a preferred embodiment of the strip of the invention, the warp yarns are folded orthogonally to the plane of the strip at each end thereof, and the weft yarns of the re-weaving zones are smaller in diameter than the weft yarns in the remainder of the strip.
By folding the warp yarns orthogonally to the plane of the strip, the size of the loops in the weft yarn direction is reduced. Nevertheless, after folding each warp yarn at one end of the strip is re-woven as extra thickness onto itself with the weft yarns in the re-weaving zone. However, the reduction in the diameter of the weft yarns in each re-weaving zone makes it possible to compensate for the extra thickness of the warp yarns so as to maintain thickness that is relatively constant for the strip over its entire length. Finally, crxc3xaaping. the weft yarns during the operation of thermofixing the weft yarns and the warp yarns at high temperature makes it possible to reduce any difference in thickness between the re-weaving zones and the remainder of the strip.
In yet another preferred embodiment, the warp yarns re of flat section thus making it possible to reduce marking on the sheet of paper and to reduce the permeability of the strip.